August 1, 2008

Tiny Star Turns Heavyweight

In the beginning, scientists say the first star to appear after the Big Bang quickly grew into a monster 100 times more massive than the sun.

U.S. and Japanese researchers say the first cosmological object formed in the universe was a tiny protostar with a mass of about 1 percent of our sun. Scientists spent years developing a complex computer simulation of what it was like after the Big Bang that formed the universe.

"The first stars were very different from stars like the sun," explained Harvard astronomy professor Lars Hernquist, co-author of a paper describing the findings in Friday's issue of the journal Science.

Hernquist said, the sun is mostly hydrogen, and it also contains oxygen and carbon. The early stars were primarily hydrogen and helium, and were much more luminous and had a shorter life.

"These differences have important implications for what happened afterward," he said.

Naoki Yoshida of Nagoya University in Japan said this protostar grew to 100 times the sun's mass over about 10,000 years; rapid growth even on a cosmic scale.

The study found the first generation of stars seemed to have lived hard and died quickly. Researchers found these stars only lived about one million years, while our sun may live 5 billion years.

Scientists think the universe began in a Big Bang explosion 13.7 billion years ago and has been expanding ever since. However, some have struggled to understand how the first stars formed in the aftermath of this cataclysm.

"This general picture of star formation, and the ability to compare how stellar objects form in different time periods and regions of the universe, will eventually allow investigation into the origins of life and planets," Hernquist said.

Japanese and U.S. astronomers ran a sophisticated computer simulation that showed how some of the hydrogen and helium gases strewn throughout the young universe came together to form the first generation of stars.

"These stars are thought to be the first sources of light and also the first sources of heavy elements such as carbon, oxygen and iron," said Yoshida.

"If we want to understand how things came about and look the way they do now, we have to go back in time and understand how stars looked when they first began to form," added Hernquist.

At the time, the universe was about 20 times as compact as it is now. "We think that early in the universe, the only elements that existed were hydrogen and helium, with trace amounts of lithium," Hernquist said.

Researchers said this matter was generally very smoothly distributed throughout the universe, but some regions had greater concentrations of it than others.  Gravity drew in more and more material over time, setting in motion clouds of hydrogen and helium that came together as a "protostar" -- the seed of a much larger star.

The study may prove to be a "Cosmic Rosetta stone" suggested Volker Bromm, an assistant astronomy professor at the University of Texas.

Bromm said the findings could potentially help researchers unlock the process of star formation, much as the Rosetta stone led to the understanding of ancient Egyptian writing.

The first protostar was born about 300 million years after the Big Bang, the researchers said. While none of the stars survive today, their influence remains.

Hernquist said these stars may have ceased to exist in a very bright supernova or might have collapsed in on them selves. He believes they formed black holes with a tiny amount of material ejected into space as ingredients for future stars.


Image Caption: The computer simulation designed by Dr. Yoshida et al. demonstrates how gas and dust came together in the early universe to form the first stars after the Big Bang. Credit: Photo provided by Dr. Naoki Yoshida of Nagoya University in Japan via Science-AAAS


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